The USENIX Security conference has been warned that by tweaking the firmware on certain kinds of phones, a hacker could make it so other phones in the area are unable to receive incoming calls or SMS messages.
The hacker modifies the baseband processor on some Motorola phones and tricking some older 2G GSM networks into not delivering calls and messages. The hack could shut down some small localised mobile networks by spying on the messages sent from phone towers and not delivering them.